PeerConnection(java): use MediaCodec for HW-accelerated video encode where available.

Still disabled by default until https://code.google.com/p/webrtc/issues/detail?id=2899 is resolved.

Also (because I needed them during development):
- make AppRTCDemo "debuggable" for extra JNI checks
- honor audio constraints served by apprtc.appspot.com
- don't "restart" video when it hasn't been stopped (affects running with the
  screen off)

BUG=2575
R=noahric@google.com

Review URL: https://webrtc-codereview.appspot.com/8269004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5539 4adac7df-926f-26a2-2b94-8c16560cd09d

talk/examples/android/AndroidManifest.xml

@@ -17,6 +17,7 @@
 
   <application android:label="@string/app_name"
                android:icon="@drawable/ic_launcher"
+               android:debuggable="true"
                android:allowBackup="false">
     <activity android:name="AppRTCDemoActivity"
               android:label="@string/app_name"